No abstract

No abstract

Shock layer radiation is observed in the wavelength range from vacuum-ultraviolet (VUV) to near-infrared (NIR) using a free-piston double-diaphragm shock tube. In the VUV region, atomic lines of N and C are predominant and no molecular band spectra are seen. In the ultraviolet (UV) region, the molecular bands of N 2 (2þ) and N 2 þ (1À) systems are predominant. In the visible (VIS) and NIR regions, atomic lines of N are intense, and weak molecular bands of the N 2 (1þ) system are seen. The spectrum in the VUV region becomes more intense than that in the UV region with increasing shock velocity. On the other hand, the spectrum in the UV region is almost same with increasing shock velocity. The measured spectrum is analyzed using the radiation analysis code SPRADIAN 2. The analysis shows that the numerical spectrum can reproduce the measured one when the electronic excitation temperature is higher than the vibrational temperature. The electronic excitation temperature is evaluated from the atomic lines of nitrogen in a wide wavelength range and the spatial distribution is obtained. The result shows the electronic excitation temperature is higher than the vibrational temperature immediately behind a shock wave, consistent with the result obtained from the spectrum analysis.

Spectroscopic measurement is conducted using a free-piston double-diaphragm shock tube to investigate the nonequilibrium phenomena in the shock layer. The shock velocity and spectrum position correlated to the shock front are determined using a double-laser schlieren measurement system for precise localization. Emission spectra of N 2 (1þ), N 2 (2þ) and N 2 þ (1À) band systems are obtained by means of time-frozen imaging spectroscopy. A spectrum fitting method is used to determine the rotational and vibrational temperatures from the measured spectra, and temperature distribution correlated to the shock front is finally obtained. The measured rotational temperatures are in high nonequilibrium with the translational temperature expected from the numerical prediction of the two-temperature model. The measured rotational temperature for N 2 (2þ) is lower than those for N 2 (1þ) and N 2 þ (1À) immediately behind a shock wave. Hence, rotational relaxation for the N 2 C state looks slower than those for the N 2 B and N 2 þ B states. On the contrary, the measured vibrational temperatures for N 2 (1þ), N 2 (2þ) and N 2 þ (1À) are close to each other, and agree well with the numerical prediction of the two-temperature model. The experiment and numerical analysis suggest that the electronic excitation temperature is in nonequilibrium with the vibrational temperature.Key Words: Shock Tube, Re-entry, Nonequilibrium, Shock Wave, Emission Spectroscopy Nomenclature L: spectrum position from the shock front, mm n: number density, particles/m 3 P 0 : ambient pressure ahead of shock wave, Pa T t : translational temperature, K T r : rotational temperature, K T v : vibrational temperature, K T ex : electronic excitation temperature, K V: shock velocity, km/s

The objective of this research is to demonstrate the advantage and characterize the thrust performance and the induced flow field generated by the TED plasma actuator with serrated electrode. The induced body force of the serrated TED plasma actuator was investigated on quiescent air, by measuring thrust of the induced jet. A time-resolved PIV was used to acquire a velocity field. From the results of the thrust measurement, it is confirmed that the serrated TED plasma actuator enhances the thrust compared to the straight-edge TED plasma actuator. The serrated TED also had a significantly better efficiency regarding power consumption compared to the straight-edge TED. From the PIV analysis, it is clearly found that the serrated TED plasma actuator generate uniform facing jet from both of the electrode, by the uniform generation of the plasma from the sawtooth vertexes.